1. Field of Invention
This invention relates to solving a Sudoku puzzle of any difficulty level;                by quickly setting up in place ‘given-numbers’ of a puzzle on the apparatus;        by quickly setting up all solution possibilities at all ‘single-squares’ at once;        by helping to quickly find the single-digit solutions at single-squares;        by helping to retract any errors made and retrace without a fresh start-over;        by helping to clearly identify always the ‘given-numbers’ apart from the ‘arrived-numbers’ (i.e. the only possible single-digit solution numbers);        by helping to solve the entire puzzle without need of any writing and erasing aids;        by allowing repeated usage of the apparatus for new puzzles;        by helping to solve difficult puzzles faster and yet not diminish the challenges of logical thinking required;        By helping to instill courage to solve very difficult puzzles till the end.        
Sudoku is a popular puzzle, with a set of a few ‘given-numbers’ at start that are assigned specific locations to ‘single-squares’ which are set up as a 9×9 pattern of 81 single-squares. The single-squares are grouped further, with the outer boundaries of each group being visually distinct, as clusters of nine (3×3=9) single-squares forming total of 9 square ‘regions’. Only single-digits chosen from 1 through 9 can occupy any single-square, whether given or arrived number. The object is to solve the puzzle by finding single-digit numbers for all the empty squares, while observing the rule that no row, no column, and no ‘region’ within it has a repeated digit.
Having been supplied a set of ‘given-numbers’, their quantity, positioning, and values determine the level of difficulty of solving a given puzzle.
2. Prior Art
Prior art for Sudoku puzzle solving utilizes methods that have disadvantages.
Disadvantages of Prior Art:
                1 It presents the puzzle solver blank squares requiring writing in;        2 It most often requires writing aids, raising possibility for errors;        3 It most often requires erasing and writing aids, to correct errors;        4 When an error is discovered, backtracking is difficult and messy;        5 The apparatus often is for one use only and then it is discarded;        6 Any reusable apparatus is tarnished with frequent writing and erasing;        7 Frequent erasing and correcting taxes the thinking process required, and may instill discouragement with partially solved puzzles left behind;        8 An electronic apparatus may tend to have helping logic software which may negate the challenge of logical thinking that is to be encouraged;        9 Error making being a normal frequent human experience, difficult puzzles become daunting and discouraging;        10 Difficult puzzles are very often left not attempted robbing one of mental and visual exercises and the discipline of logical thinking.        
3. Objects and Advantages
Present invention utilizes a Sudoku solving apparatus accommodating the 81 single-squares for the ‘arrived-numbers’ plus the ‘given-numbers’.
However in the present invention, each single-square contains 9 subareas, with each single-square containing all the single-digits from 1 through 9, one digit per subarea with no repetition of digits, and with means for digits being at-display or at no-display for every digit individually.
Hence present invention requires no writing aids.
Present invention requires no erasing aids.
At start in each single-square designated as a location for a ‘given-number’ its 8 non-matching digits can be set to ‘no-display’ leaving only the matching digit at at-display.
For any particular single-square needing an ‘arrived-number’ solution, that square's non solution digits can be set to no-display through logic by the means provided, and as more digits are identified to be not the solutions those digits can be set at no-display. The process continues until every single-square has 8 digits at no-display.
At any time each ‘arrived-number’ can be back tracked and checked for its accuracy as a solution. In case of errors discovered, the no-display status of any required digits can be changed to at-display and the logic process reapplied.
As the puzzle solving continues, It is possible to simply leave any only remaining digit at-display in its single-square to remain so, and proceed solving for the other single-squares. But, since a single-digit occupies only 1/9th of a single-square and may appear inconveniently small, a separate larger full single-square size ‘number-pad’ may be snap-installed as an overlay at a single-square. This prominently visible number-pad, meant to occupy a single-square, can mask all the 9 digits of a single-square, whether they be at-display or at no-display. This snap-installation can be even used at start for the ‘given-numbers’ also.
It is suggested that the two types of number-pads (‘arrived’ versus ‘given’) appear different from each other in some significant way, so as to recognize them by their differences while puzzle solving is in progress. This recognizing shape difference between number-pads can be interchanged without any change in functionality.
In case of an electronic/electrical board, the statuses of at-display and no-display of digits will equivalently be ‘switch on and switch off’ statuses.
For an electronic display pad, it could be just a matter of resizing to a larger size the text size of each of the only digit that is to occupy a given single-square and adjust the text format as a means of differentiating between the two types, namely given versus arrived.
For an electrical display pad (or for that matter, for an electronic one also) the snap-installation of larger overlay number-pads can also be used.